No Need to Worry
The Podtrac website is getting a malware warning. They know about it, and are working to fix it.
Meanwhile, rest assured, even though you may get this warning when downloading TWiT shows via a browser (we redirect through Podtrac to get audience numbers) the MP3 and MP4 files are safe.
Downloads from iTunes, Stitcher, the TWiT apps, etc. are safe and unaffected.